The field of the present invention is motorcycles and the structure and exhaust systems therefor.
Motorcycles require generally compact structure and design for all components to insure a compact overall assembly. Somewhat in conflict with the requirement for compactness is the advantageous arrangement of the exhaust pipes to have each pipe extending from a cylinder or cylinders be of equal length. With multicylinder V-type engines with a forward cylinder block and a rear cylinder block, the exhaust ports from the blocks are widely separated. Additionally, it is desirable to have the exhaust from the engine directed aft behind the rider or riders. As a result, the exhaust from the forward engine block must travel a substantially greater horizontal distance than the exhaust from the rear engine block. This arrangement is detrimental to a system having equal length exhaust pipes.
In conjunction with the compact motorcycle design, the exhaust system is desirably placed so that it is not extending laterally in a manner which would interfere with or come too close to the legs of the rider or riders. Often, the exhaust is directed low on the vehicle to avoid any such interference. Once again, such arrangements restrict the ability of the exhaust system to accommodate equal length exhaust passages.
The frames of motorcycles must also be designed for compactness and compatibility with the equipment fixed thereon. Generally extending from the head pipe is a main frame member and a down tube or down tubes. These elements are connected behind the engine by center frame members extending to a mount for the rear suspension. A back stay structure extends from the center frame upwardly and rearwardly to support rear frame members which in turn support the seat and provide an attachment for the rear suspension cushion members. The exhaust systems must extend around or below such a structure. Additionally, mechanical elements must be fixed to the frame for support. This includes the exhaust system as well as the engine, the seat and the like. Pillion steps for a passenger often are fixed to the back stay structure of the motorcycle. Such structural attachments must be securely and rigidly fixed in position. The addition of such elements can result in reduced structural strength of the frame member to which it is welded or otherwise affixed. Consequently, it is necessary to provide a truly integrated motorcycle design to achieve appropriate strength, compactness and function.